Composition and method for removing sulfide-containing scale from metal surfaces

Abstract

Sulfide-containing scale is removed from metal surfaces by contacting the encrusted surface with an aqueous acid cleaning solution having an aldehyde (e.g., formaldehyde) dissolved or dispersed in the acid in an amount sufficient to prevent the evolution of hydrogen sulfide gas.

We claim: 
     
       1. A method of chemically cleaning acid-soluble, sulfide-containing scale from a metal surface comprising contacting said scale with an aqueous acid cleaning composition comprising an aqueous non-oxidizing acid having at least one aldehyde dissolved or dispersed therein, which aldehyde is present in an amount at least sufficient to prevent or substantially prevent the evolution of hydrogen sulfide gas. 
     
     
       2. The method defined by claim 1 wherein said acid is hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, glycolic acid, or citric acid. 
     
     
       3. The method defined by claim 2 wherein said acid is hydrochloric acid or sulfuric acid. 
     
     
       4. The method defined by claim 1 wherein said aldehyde is formaldehyde, paraformaldehyde, acetaldehyde, glyoxal, beta-hydroxybutyraldehyde or methyl-3-cyclohexene-carboxaldehyde. 
     
     
       5. The method defined by claim 1 wherein said acid is sulfuric acid and wherein said aldehyde is formaldehyde. 
     
     
       6. The method of claim 1 additionally comprising a compatible acid-corrosion inhibitor. 
     
     
       7. The method of claim 5 additionally comprising a compatible amine-based corrosion inhibitor. 
     
     
       8. An aqueous acid composition comprising an aqueous acid having dissolved or dispersed therein at least one aldehyde; said composition having, as one of its chemical properties, the capability of dissolving acid-soluble, sulfide-containing scale from a metal surface without the evolution of hydrogen sulfide gas, provided that the aldehyde is present in excess of the acid required to dissolve the sulfide containing scale. 
     
     
       9. The composition defined by claim 8 wherein said acid is hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, glycolic acid, or citric acid. 
     
     
       10. The composition defined by claim 9 wherein said acid is hydrochloric acid or sulfuric acid. 
     
     
       11. The composition defined by claim 10 wherein said acid is sulfuric acid. 
     
     
       12. The composition defined by claim 8 wherein said aldehyde is formaldehyde or acetaldehyde. 
     
     
       13. The composition defined by claim 12 wherein said aldehyde is formaldehyde. 
     
     
       14. The composition defined by claim 11 wherein said aldehyde is formaldehyde. 
     
     
       15. The composition defined by claim 8 additionally comprising a compatible acid corrosion inhibitor. 
     
     
       16. The composition defined by claim 14 comprising a compatible amine-based corrosion inhibitor. 
     
     
       17. The composition defined by claim 14 wherein the concentration of said sulfuric acid is from about 5 to about 15 percent and said formaldehyde is present in excess. 
     
     
       18. The method defined by claim 1 wherein said aldehyde is an aliphatic aldehyde. 
     
     
       19. The method defined by claim 1 wherein the temperature of the aqueous acid cleaning composition is from about 140° to about 160° F. 
     
     
       20. The method defined by claim 5 wherein the temperature of the aqueous acid cleaning composition is from about 140° to about 160° F. 
     
     
       21. The method defined by claim 1 wherein said aqueous acid cleaning composition is generated in situ by adding an aqueous non-oxidizing acid to an aqueous composition having at least one aldehyde dissolved or disbursed therein which in contact with said acid-soluble sulfide-containing scale.